Ant predators of the Western spruce budworm (Choristoneura occidentalis Freeman) : species composition and patterns of occurrence in eastern Oregon and western Montana PublicDeposited

Descriptions

The identity and distribution of ant species preying on the
western spruce budworm (Choristoneura occidentalis Freeman) was
investigated in eastern Oregon and western Montana. A sticky trap was
developed to index ant foraging activity in the canopy by intercepting
ants falling from the tree as they traveled between canopy and
ground. For all common ant species, trap catches were highly
correlated with the average number of ants moving up the tree bole.
Thus, traps indexed both species composition and density of ants
foraging in the canopy.
Ant species preying on pupae of the budworm were investigated on
2 sites in eastern Oregon in 1981, and 4 sites in eastern Oregon and 6
sites in western Montana in 1982. Predation was observed by checking
pupae stocked on trees actively foraged by ants.
The following ant species and numbers were collected as they fed
on budworm pupae: Camponotus modoc Wheeler, 160; C. laevigatus
(Smith), 53; C. vicinus Mayr, 48; Formica obscuripes Forel, 174; F.
podzolica Francoeur, 43; F. accreta Francoeur, 32; F. neorufibarbis
Emery 12; F. lasioides Emery, 1; F. sp. (microgyna group), 1.
Camponotus species dominated the Oregon collections, and F. obscuripes
dominated the collections in Montana.
The distribution of canopy foraging ant species was studied on 24
sites in Montana and 24 sites in Oregon. Sites were selected along a
moisture-temperature gradient indexed by vegetational composition
(habitat type). Ant foraging activity was measured using sticky
traps, and several site and stand variables were correlated with the
abundance of ants collected at each site.
Nine species of Formica and Camponotus were collected in Montana
and 11 species in Oregon. Four species were common in both states--C.
modoc, C. vicinus, F. neorufibarbis, and F. podzolica. In addition,
C. herculeanus (L.) was common in Montana and F. accreta was common in
Oregon. The distribution of these species varied among habitat types
and between states and the abundance of each was correlated with a
different set of environmental variables. At least one ant species
predaceous on the western spruce budworm was common in each habitat
type in either state. Across almost all habitat types, each common
species was more abundant in stands where average canopy coverage was
less than 90%. The distribution of ant foragers in the canopy on
each plot was highly aggregated in all species in either state.